Method of and apparatus for stretching metal strips



Dec. 21, 1943. HUNTER 2,337,047

METHOD OF AND APPARATUS FOR STRETCHING METAL STRIPS Filed June 19, 1959 2 She etsSheet 1 r E P FIG. 6. INVENTOR.

Jain-w L. AMA/r52 ATTORN Y.

,Dec.Z1,1943. S J, L.HUNTER 2,337,047

METHOD OF AND APPARATUS FOR STRETCHING METAL STRIPS I Filed June 19, 1939 2 sheets sheet 2 INVENTOR. L/OSEPH A. fi/u/vme ATTORNE Patented Dec. 21, 1943 METHOD OF AND APPARATUS FOR STRETCHING METAL STRIPS Joseph L. Hunter, Riverside, Calif assignor to Acme Steel Company, Chicago, Ill., a corporation of Illinois Application June 19, 1939, Serial No. 279,891

8 Claims.

This invention relates to an improved method of and apparatus for treating long metal strips by selectively stretching longitudinally one or more different laterally displaced portions of the strip, such as the central portion and the lateral edge portions thereof, in order to produce a strip which is straight and substantially flat or buckled or possessed of some other desired surface contour, which product may be formed and used with particular advantage in the manufacture of Venetian blind slats.

Except for the method described and claimed stresses into the metal with a result that the strips so formed are warped and crooked and present wavy edges. The strips which are cut from the edge of the sheet are also invariably bowed outwardly in the plane of the sheet. Strip material of this character is totally unsuited for applications which require flatness and straightness such as that required in the manufacture of metal Venetian blind slats.

Many unsuccessful attempts have been made in the past to remove these internal stresses and to straighten and fiattan the strip material by such methods as reworking the strip by rolling them on rollers. The use of crowned rollers helps to improve the straightness and flatness but requires extremely accurate control of the tension to which the strip is subjected as it is fed through these rollers. None of the prior attempts have provided long metallic ribbons which are free from internal stresses and which are uniformly fiat and straight.

It is an object of the present invention to provide an improved method and improved apparatus for stretching longitudinally one portion of a metal strip such as the intermediate portion thereof.

It is also an object of my invention to provide an elongated metal strip which has its center portion and edge portions stretched sufiiciently to produce a, predetermined condition of the internal stresses and provide a straight piece of material which is flat or of other desired surface contour.

It is also an object of my invention to provide a method of stretching and straightening strip metal which consists in selectively stretching the center and edges thereof longitudinally.

A further object of the invention is to provide an improved method of treating a long metal strip by stretching longitudinally the intermediate portion of the strip to produce a product which is buckled or wavy between its edges and which may be treated by the apparatus herein described or by the apparatus employed in the practice of the second stage of the process described and claimed in said Wilson Letters Patent for producing a Venetian blind slat or other product which is straight and has the desired surface contour. Y

It is also an object of my invention to provide a die through which strip material may be drawn to stretch the center portion thereof or the edges, as desired.

An additional object of my invention resides in the provision of a die which may be employed for stretching both the center portions and the edge portions of strip material.

It is also an object of my invention to provide a die for selectively stretching the center and edges of strip material with a means for independently adjusting the amount of stretch imparted to the center and to the edges.

It has been found, however, that if perfectly straight and flat strip steel is deformed by rolling to provide a curved, transverse cross section for use as a Venetian blind slat, the finished slat will be curved or bowed along its length.

It is accordingly a still further object of my invention to provide a method of forming Venetian blind slats which consists in stretching the center of the strip material longitudinally in an improved manner and then simultaneously deforming the strip transversely to produce a curved cross section while stretching the edges of the strip longitudinally to provide a straight slat free from warps.

Other objects and advantages of my invention will be apparent from a study of the following specifications, read in connection with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic representation of one method which may be employed to balance the internal stresses in strip material to provide the desired straightness and flatness thereof;

Fig. 2 is an elevation of a die which may be employed in the method illustrated in Fig. 1 and which is adapted to stretch the edges of the strip material;

Fig. 3 is a view similar to Fig. 2 showing the dies thereof set for stretching the center portion of the strip material;

Fig. 4 is a view similar to Figs. 2 and 3 but illustrating the construction of a die which may be used for substantially simultaneously stretching both the center and edges of strip material;

Fig. 5 is a vertical longitudinal section taken through the die illustrated in Fig. 2 to show the relationship between the die parts and the strip material which is fed therethrough;

' Fig. 6 is'an end elevational view of the die blocks illustrated in Figs. 2 through showing the transverse shape of the slot through which the strip material is fed;

Fig. 7 is an elevational view of a Venetian blind slat forming machine of the type described in my copending application, Serial No. 176,048, filed November 23, 1937, Patent No. 2,262,550, dated November 11, 1941, modified to include means for simultaneously stretching the edges of the strip material while it is being formed to produce the curved cross section therein;

Fig. 8 is an enlarged fragmentary elevational view of the forming and'stretching rollers employed on the machine illustrated in Fig. '7;

Fig.- 9 is a cross section taken substantially along the line IX-E of Fig. 8 to show the transverse shape of the strip material as it is fed into the stretching and forming mechanism;

Fig. 10 is a cross sectional view taken substantially along the line X--X of Fig. 8 illustrating the relative curvatures of the strip material and the stretching roller over which it is fed;

Fig. 11 is a cross sectional view taken substantially along the line XIXI of Fig. 8 illustrating the manner in which the strip material is deformed by the forming and feeding rollers employed on the machine illustrated in Fig. 7;

Fig. 12 is a cross sectional view taken substantially along the line XII-XII of Fig. 8 to show the relative curvature of the strip of material and the guiding roller over which it' is fed; and

Fig. 13 is a cross sectional view taken substantially along the line XIIIXIII of Fig. 8 to show the final desired cross section which is imparted to the strip of material by the combined stretching and deforming process.

Referring to the drawings, Fig. 1 is a diagrammatic representation illustrating the preferred manner in which stock strip material may be manipulated. to balance the internal stresses normally present therein. In the practice of this method a ribbon or strip of metal, such as steel I may be fed from a reel or substantially continuous source of supply 2 over a guiding roller 3 and a drag roller 4. From the drag roller 4 the strip I is preferably fed through dies 5 and between feed rollers 6 and 7 and thence onto a takeup reel 8.

The feed rollers I5 and I may be driven by any suitable driving means so as to pull the strip material I from the storage reel 2 over the drag roller 4 and through the dies 5. Suitable takeup mechanism, such as a slip clutch, spring belt, or other device may be employed for driving the rewind reel 8 to recoil the strip material as fast as it is fed from the feeding rollers 6 and I.

The drag roller 4 is preferably shod with friction material so as to provide a firm frictional engagement with the strip I as it is fed thereover. A suitable adjusting means such as a hand wheel 9 may be employed for imparting a frictional drag, tending to prevent rotation of the drag roller 4 so as to subject that portion of the strip I which is drawn through the dies 5 to any desired tension,

The dies 5 are preferably constructed along the lines illustrated in Figs. 2 through 6 and include two or more die block assemblies 5a which may comprise an upper'die shoe I0 and a lower die shoe I I which are held in spaced relationship-relative to each other by means of side supporting plates I2 and I3, The supporting plates I2 and the upper die shoe I0.

I3 may be secured to the shoes I0 and II by means of screws or other suitable securing device I4. The upper shoe I0 is preferably formed with a concave partially cylindrical surface I5 adapted to coact with a concentrically disposed convex cylindrical surface I6 which is formed on the lower die shoe II to provide a longitudinally extending slot having an arcuate cross section and adapted to receive, in a lengthwise fashion, the strip of steel I.

Each of the die blocks 50. is preferably supported between an upper supporting plate I? and a lower supporting plate I8 by means of pivot screws or bolts I9 which are threadedly engaged with the side plates I Z and I3 and mounted for rotation in side spacer blocks 20 extending between the upper and lower supporting plates I1 and I8.

In order that the angular position of the slot which is defined by the upper and lower die shoes Ill and II may be adjusted relative to the plane of the supporting plate I8, I provide a lower adjusting screw 2i which is threadedly engaged with the lower supporting plate I8 and adapted to bear against the central portion of the lower die shoe II and cooperate with a pair of similar adjusting screws 22 and 23 threadedly engaged with the upper supporting plate I! and disposed in a position bearing against opposite ends of It will be observed that the three adjusting screws 2I, 22 and 23 may be so manipulated as to securely lock each of the die blocks 5a into any position providing the desired angularity between the length of the strip receiving slot therethrough and the lower supporting plate I8.

I have illustrated in Fig. 2 the manner in which a pair of die blocks 5a are set when it is desired to stretch the edge of a strip of material I which 40 is fed therethrough. The operation of the die effecting the stretching of the edges of the strip may be readily understood by having reference to Fig. 5 in which it will be observed that due to the opposite positioning of the die blocks 5a employed as regards the direction of the strip receiving slot therethrough, the distance between the die blocks at the center of the strip of material is less than the distance between these blocks at positions occupied by the edges of the strip.

It will be observed that if the strip I is fed through these blocks in a direction indicated by arrow 24 in Fig. 5, all parts of the strip must pass simultaneously and at the same rate through the left hand one of the die blocks 50. and in the same manner all parts of the strip I must pass simultaneously through the right hand one of these die blocks. It will be observed, however, that in passing in the space between the left hand die block and the right hand die block, the edges of the strip must be moved through a greater distance than is the center. It will be readily observed that this greater travel of the edges of the strip may only be accomplished by stretching these edges.

I have illustrated in Fig. 3 the manner in which a pair of the die blocks 5a are set when it is desired to stretch the center of the strip of material without stretching the edges thereof. It will be observed that in this figure, the die blocks are disposed in the opposite positions from those illustrated in Fig. 2 so that as the strip I is passed from the left hand one of the blocks to the right hand one of the blocks, the center thereof must be moveda greater distance than the edges so Fig. 4 illustrates the manner in which three die blocks may be employed for substantially simulvtaneously stretching both the edges and the center of the strip. It will be observed that with this type of die set-up, the left hand and center ones of the blocks 5a operate as a pair in the same fashion as does the set-up in Fig. 2 to stretch the edges of the strip and that the center one of the blocks and the right hand one can operate in the same fashion as does the pair illustrated in Fig. 3 to stretch the center portion of the strip.

It will be observed that I have provided, by means of the apparatus just described, a method of selectively stretching both the center and the edges of strip material and in which the amount of stretch which is imparted to the center and the edges may be adjusted at will.

While I have referred to the action of the dies as efiecting a stretching of the strip and the treated strip as having portions thereof stretched, it will be observed that all portions of the finished strip may be substantially the same length, the stretching merely operating to impart permanent stresses to the material. Attention is called to the fact that a,centerstretched strip has its edge portions stressed longitudinally in tension by compression forces in the center portion and that an edgestretched strip has its center portion stressed longitudinally in tension by longitudinal compression stresses in the edge portions.

It has been found that ordinary commercial strip material which is very crooked-and warped may, by imparting the correct amount of center and edge stretch, be converted into an absolutely fiat and straight piece of material. Itis understood that other types of dies or other mechanisms may be employed for imparting this stretching of the center and the edges of the material .and I do not intend to be limited to the particular device illustrated and described.

As pointed out hereinbefore, it has been found that if an absolutely fiat and straight strip of material, such as that which is provided by imparting the required amount of center and edge stretch to commercial strip material, be deformed transversely to provide a curved cross section of the type employed in metal Venetian blind slats, the slat thus formed will, due to the transverse deformation thereof, curve or bow longitudinally so as to provide a somewhat unsatisfactory slat.

I have illustrated in Fig. '7 a machine which may be employed for forming Venetian blind slats which are absolutely straight andfree of bows and warps. This machine is preferably constructed along the lines .described and claimed in my copending application Serial No. 176,048, filed November 23, 1937, Patent No. 2,262,550,

- dated November 11, 1941, which includes a supporting structure which carries a cutting and punching mechanism 3| adapted to receive strip material 32 as it is fed theretofrom feeding and deforming rollers 33 and 34.

I have found that when absolutely flat and straight strip material is deformed transversely by the feeding and deforming rollers 33-34 to ing flat strip material, material is employed which has been previously center stretched in the manner described hereinbefore and this material is simultaneously edge stretched and deformed transversely to provide the desired curved cross section, the resulting Venetian blind slat will be free of bows and warps.

The mechanism whichmay be employed on themachine illustrated in Fig. 7 for accomplishing this final deforming and edge stretch-ingot the material is illustrated in Fig. 8 in which the forming rollers 33 and 34 are disposed so that their point of tangency is lower than the horizontal line through the cutting and punching dies 3|. In order that the strip of material 32 may be accurately fed through the dies 31, I employ an idler or guiding roller 35, the upper surface of which is disposed tangent to theline extending through the dies 3|. I dispose on the opposite side of the feeding and deforming rollers 33-34 an edge stretching roller 36 which may be mounted for rotation about a horizontal axis by means of a shaft 31 which is carried in a shaft bearing 38.

Vertical adjustment of the roller 36 may be obtained by mounting the shaft bearing 38 in a yoke structure 39 carried by the machine supporting framework 30 and by providing upper and lower set screws 40 and M which are threadedly engaged with the yoke 39 and disposed in a position to bear against the upper and lower surfaces of the bearing 38. I It will be observed that proper manipulation of the set screws '40 and M will effect a raising and lowering'of the axis of rotation of the stretching roller 36 so that the upper edge thereof may be disposed at any desired height above a horizontal line passing through the point of tangency of the deforming rollers 33 and 33.

The strip material 32 is preferably center stretched prior to its use with this machine and a reel of previously center stretched material may be supported upon a suitable supporting framework 42.

produce the desired curved cross section therein,

the material will be bowed downwardly at its ends, being'discharged from the rollers 33 and 34 along a path indicated by dotted lines in Fig. 8.

I have found, however, that if insteadof'employ- The stretching roller 36 and the guiding roller 35 are provided with convex rims, as illustrated in Figs. 10 and 12 so that as the strip material is fed thereover it engages the rollers 35 and 36 at the center portion only, leaving the edges thereof free to move upwardly or downwardly relative to the center section as conditions of operation may require.

The forming rollers 33 and 34 are preferably formed with complementary curved cross sections adapted to clamp the strip of material 32 securely therebetween in the manner illustrated in Fig. 11 to stretch the material beyond its elastic limit and permanently deform the material into a curved cross section as illustrated in Fig. 13. In operation, the point of tangency on thelateral center of the feeding rollers 33 and 34 is disposed below a line joining the upper surface of the stretching roller 36 and the guiding roller 35 so that as the material is passed between the rollers 33 and 34, the path of movement of any portion disposed at the edge; of the strip is longer than the path of movement of a-corresponding portion of the center thereof. It will be observed that this operates to stretch the edges of the strip material, the amount of such stretching being controlled by the amount the point of tangency of the feed rollers 33 and 34 is disposed below the line joining the upper surface of the stretching roller 36 and theguiding roller 35. This amount of nus-alignment may be controlled at will by changing the vertical positioning of the stretching roller 36 by means of the set screws 40 and II in the manner previously described.

From the foregoing, it will appear that I have provided a method of deforming a commercial strip material so as to provide a straight Venetian blind slat having a curved cross section. It will also be observed that by stretching the center of the strip material before it is used on the Venetian blind slat forming machine, the machine will operate to stretch the edges of the material as it is formed transversely to provide just the right amount of deformation, resulting in the production of a Venetian blind slat which is perfectly straight and free from bows and warps.

While I have illustrated the use of rollers as a means for imparting the edge stretch to the material, it is to be understood thatother devices, such as dies or the like, may be used to provide the requisite amount of edge stretch as the material is deformed transversely.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details of construction shown or described herein, except as defined in the appended claims.

I claim:

1. In apparatus for stretching a longitudinal portion of a long substantially fiat metal strip,

the combination of a pair of die blocks each of I which includes means defining a straight lengthwise extending slot having a bowed cross section and a width and height substantially equal to the width and thickness of said strip, means mounting said die blocks in fixed spaced end to end relation to each other with the direction of the length of one of said slots disposed at an angle to the direction of the length of the other of said slots, and means for feeding said strip longitudinally through both of said slots for effecting the longitudinal stretching of aportion of the width of said strip with respect to a similar adjacent portion thereof, said slots in the two die blocks being bowed in the same direction and to such an extent as to maintain the transverse stresses in said strip below the elastic limit of said metal.

2. In an apparatus for stretching a longitudinal portion of a long substantially fiat metal strip throughout its length with respect to other longitudinal portions thereof, the combination of: three die blocks, each of which includes a means defining a straight lengthwise extending slot having a bowed cross section and a width and height substantially equal to the width and thickness of said strip; means mounting said blocks in fixed spaced end to end relation to each other with the length of said slots in said end blocks disposed in substantially the same direction and the length of said slot in the center block disposed at an angle thereto; and means for feeding said strip longitudinally through all of said slots for substantially simultaneously stretching longitudinally both the center and adjacent edge portions of said strip.

3. The combination in apparatus for stretching a longitudinal portion of a long substantially flat metal strip,'of a plurality of sets of die blocks each having a longitudinal passage therethrough which is of such non-planar cross section transversely of the strip that said strip may be moved through said'passages without eflecting the permanent transverse forming of the strip, said pasinclined longitudinally sages in said die blocks being relatively inclined longitudinally.

5. The method of permanently stretching an elongated metal strip in one longitudinal portion thereof which consists in feeding the strip endwise and maintaining longitudinal tension there in, confining the moving strip while so under tension in successive stages of its progress to prevent transverse displacement thereof and to impart to the strip a non-planar cross section in each of said stages, and spacing said stages apart through at least a part of the width of the strip and causing the paths of travel of said strip in successive stages to be relatively inclined, whereby difierent portions of the Strip which are relatively inclined are compelled to follow paths of travel of different lengths in passing from one of said stages to the other.

6. The method of permanently stretching an elongated metal strip in one longitudinal portion thereof, which consists in feeding the strip endwise and maintaining longitudinal tension therein while moving the strip through a plurality of successive longitudinally straight, transversely curved confining passages which are relatively inclined longitudinally of the strip, maintaining the transversely acting stresses in the strip during said movement below the elastic limit of the metal, and compelling different portions of the strip which are laterally displaced from each other to follow paths of different lengths in passing from one of said passages to the other.

7. The method of permanently stretching an elongated metal strip in one longitudinal portion thereof, which consists in feeding the strip endwise and maintaining longitudinal tension therein while moving the strip through a plurality of successive longitudinally straight, transversely curved confining passages which are relatively of the strip, maintaining the transversely acting stresses in the strip during said movementbelow the elastic limit of the versely acting stresses in the strip during said movement below the elastic limit of said metal, and compelling diiferent portions of the strip which are laterally displaced from each other to follow paths of different lengths in passing from one of said passages to the other.

JOSEPH L. HUNTER. 

